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Can anyone recommend a good tutorial on how to get started casting miniatures in metal? There seems to be a lot of tutorials out there for resin casting but less so for metal.

Two methods - drop casting and spin casting.

Outside of a workshop environment you're likely to be drop casting.

This works by putting a large weight of metal above the casting volume into which it pours via feed channels, forcing air out of small vent channels to flood the mould cavity.

Typically drop-casting moulds are in RTV rubber, and designed 'on the flat', meaning that the models are designed with no major overhangs into the the mould which will prevent it being pulled from a 2 part mould split down the axis of the flat.

Moulds are produced similarly to the method for resin (usually a clay surface in a box into which the master and key objects (usually marbles or similar spheres) are pressed and the clay brought flush to the intended seam, coat that with a mould release agent (often vaseline) before pouring in the mould rubber. Once that side is cured the clay is removed (the master is left in the rubber but the key objects are removed) the exposed side of the mould and masteris coated with release agent and the second half of the mould is poured.

The rubber used will need to cope with the temperature of the metal, and the rigidity will vary depending on this and the requirements of your model. In general you want as rigid as you can get the master out of easily, as the weight of metal or the pressure of the mould being held between two bits of wood in a vice (usual method) will deform it if it's too soft.

The master should be aligned in the mould to minimise places where rising air can be trapped - each of these should be connected to the head volume by a wide feed channel, and exited by a narrow vent.

Pouring the mould is normally held in a normal bench vice between two wooden plates. Sometimes these are clamped in addition.

When you pour the weight of the metal in the head will force air (and eventually metal) out of the vents. When you've got metal coming out of the vents, you know your mould is full.

It's all pretty 'common sense' stuff. As with dealing with any high temperature material there's a gamut of safety caveats - don't get the mould wet is a big one. Get a proper crucible and tools (ladel, gloves, visor, heavy apron).

Thanks for the walkthrough, do you have any specific rubber to recommend for the moulding?

I did some simple metal casting as a kid with Prince August moulds so I'm not entirely unfamiliar with it, but things obviously get more advanced when you make your own moulds and want more detailed casts.

Try this shop:
https://shop.princeaugust.ie/

or this one:
https://tiranti.co.uk/products/hurst-metal-casting/

That melting pot Prince August sells seems like a pretty good deal, but I'm not sure if the metal they sell is fitting for wargaming miniatures. I'm mostly thinking of doing small scale stuff (6-15mm) I'm not sure which metal/alloy is most fitting for that.

Prince August is the most accessible.

The sell a variety of metal ingots. My metallurgy knowledge is only high-school grade but IIRC there's different compositions/ratios of the component metals which should impart different melting points and properties.

Yup.

WMAs are a "family" of alloys with similar casting properties. The various metals involved in each alloy are used for their properties.
The alloys PA sells ARE suitable for casting toy soldiers.
They aren't suitable for making teething rings.
That said, there are other WMAs available through casting supply stores that deal with the lead-free side, too.

It used to be that Tin was used for hardness, lead for detail and antimony for the flow control (in the 90s lead-free purge, bismuth replaced lead in a lot of stuff because it behaves in a similar way).
Other companies simply upped the tin content (quite a few 2nd ed gw metals were VERY tinny, leading to bits flying over the store when clipped off.)